External Libraries: Upgrade PHPMailer to version 6.6.5.
This is a maintenance release with minor changes:
* Don't try to issue `RSET` if there has been a connection error.
* Reject attempts to add folders as attachments.
* Don't suppress earlier error messages on `close()`.
* Handle `Host === null` better.
Release notes:
https://github.com/PHPMailer/PHPMailer/releases/tag/v6.6.5
For a full list of changes in this update, see the PHPMailer GitHub:
https://github.com/PHPMailer/PHPMailer/compare/v6.6.4...v6.6.5
Follow-up to [50628], [50799], [51169], [51634], [51635], [52252], [52749], [52811], [53500], [53535], [53917].
Props ayeshrajans, Synchro.
Fixes #56772.
Built from https://develop.svn.wordpress.org/trunk@54427
git-svn-id: http://core.svn.wordpress.org/trunk@53986 1a063a9b-81f0-0310-95a4-ce76da25c4cd
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